In the course of making regenerative energy sources available, more and more questions regarding a rational production of electric storage media and voltage sources, in particular high-voltage batteries (HV batteries) for electric vehicles or module strings for photovoltaic plants (PV plants), are moving to the forefront.
As an exemplary application of a production process based on the invention, the assembly process of HV batteries and of photovoltaic module strings is described first of all.
HV batteries for electric vehicles consist of individual battery modules, which are automatically connected in series during production in order to attain the required high voltage.
For this purpose, the HV batteries are most commonly set up step-by-step during the production process to form a first partial string of a module starting from a first connection (positive pole HV+) and to form a second partial string of a module starting from a second connection (negative pole HV−), a lastly installed module connecting both partial strings of the modules to each other to form a closed module string. Therefore, not until the lastly installed battery module is installed can a voltage be measured between the positive pole and the negative pole. If produced correctly, this voltage should then correspond to the desired nominal voltage of the voltage source.
In comparison to a single-string assembly, lower voltages and shorter assembly times arise in this production process since two partial strings of the modules can be assembled at the same time.
Another application of a two-string production process is constituted by the installation of photovoltaic systems, individual solar panels being connected in series in order to ultimately form a module string. Since a central connection point exists at an inverter or at a sub-distribution board, the modules most commonly are also set up as two open partial strings starting from the positive pole and from the negative pole, respectively.
Not until the last module is installed will the series connection be closed, and the desired nominal voltage rests between the positive pole and the negative pole. As long as the modules are not connected to the inverter, the (partial) strings each form an independent ungrounded power supply system. Such an ungrounded power supply system is also referred to as an isolated network (IT network, from French Isolé Terre).
When producing HV batteries as well as when constructing photovoltaic plants and when producing modularly assembled voltage sources in general, two discrete ungrounded partial systems are therefore always yielded in the described production process, said partial systems not being connected to form one individual ungrounded overall system, which provides the required nominal voltage to the connecting terminals, until the last installed module is lastly installed.
During the production process, insulation faults or line defects (line breakage) can arise in individual modules or at the electrical connections, respectively, due to mechanical stresses or through external influences and can lead to considerable losses in quality or to the uselessness of the entire production unit. The installation of initially defective modules poses a source for error. These errors should be identified and localized as soon as possible in the progression of the production process since a fault location at the end of the assembly process is connected to a considerable expenditure of time and costs.
Constant insulation monitoring is a required normative measure in many applications during later operation in the fully installed voltage source (HV battery or photovoltaic plant), however, no such monitoring is intended during production.
It is known that when assembling HV batteries via optical process control and by using robots, an attempt at optimizing the production process is made in such a manner that the failure rate is as low as possible. Only at the end of the production process will the high voltage be tested and the insulation resistance measured.
When constructing photovoltaic plants, cables, which are resistant to short circuits and have plugs protected against polarity reversal, or standardized assembly sets are used due to structural features. Damage incurred during transport or assembly errors which effect electric parameters are not identified until after the inverter has been connected. The fault location is then quite difficult depending on the installation site and the size of the photovoltaic plant.
From the state of the art, a measuring method and an assembly device for insulation testing during assembly of a high voltage battery assembled from several battery modules are known from DE 10 2014 003 325 A1. When connecting the electrical connections between the battery modules of the high voltage battery, an electrically conductive assembly tool used therefor is connected to a measuring device testing the insulation resistance. The measured insulation resistance value is compared to a reference value and should an inadmissibly large difference between the reference value and the insulation resistance value be determined, a fault signal is triggered.
From DE 10 2014 003 910 A1, a testing device for simultaneously testing several battery cells is known and comprises a measuring device for detecting a leakage current, a series voltage, a through current and/or another battery parameter. For this purpose, the testing device comprises an access network, which comprises several contacting elements for being electrically contacted to poles of the battery cells as well as at least one current bridge for electrically connecting battery cells.
However, these known methods also often prove inadequate in regard of prematurely identifying assembly errors.